Tuesday, November 18, 2008

The Krebs (Citric Acid) Cycle In Reverse

From Wikipedia, the free encyclopedia:

The reverse Krebs cycle (also known as the reverse tricarboxylic acid cycle, the reverse TCA cycle, or the reverse citric acid cycle) is a sequence of chemical reactions that are used by some bacteria to produce carbon compounds from carbon dioxide and water.

The reaction is basically the Citric acid cycle run in reverse. Where the Krebs cycle takes complex carbon molecules in the form of sugars and oxidizes them to CO2 and water, the reverse cycle takes CO2 and water to make carbon compounds. This process is used by some bacteria to synthesise carbon compounds, sometimes using hydrogen or sulphates as electron donors.[1][2] In this process it can be seen as an alternative to the far more common photosynthesis production of organic molecules.

The reaction is one of the possible candidates for prebiotic early earth conditions and so is of interest in the origin of life research. It has been found that some of the steps can be catalysed by minerals.[3]


[1] Evans MC; Buchanan BB; Arnon DI (April 1966). "A new ferredoxin-dependent carbon reduction cycle in a photosynthetic bacterium.". Proc Natl Acad Sci U S A. 55 (4): 928–34.

[2] Buchanan BB; Arnon DI. (1990). "A reverse KREBS cycle in photosynthesis: consensus at last.". Photosynth Res 24: 47–53.

[3] Xiang V. Zhang; Scot T. Martin (December 2006). "Driving Parts of Krebs Cycle in Reverse through Mineral Photochemistry". J. Am. Chem. Soc. 128 (50): 16032–16033.